The invention pertains to a method and apparatus for applying resilient surfaces to be used for running tracks, tennis courts, playgrounds, jogging paths, ballfield warning tracks and other activity areas requiring resilience.
Many materials and methods of application have been used to produce all-weather surfaces for the aforementioned uses, including pre-manufactured and in situ types. These systems typically involve a mixture of rubber granules, which provide resilience and traction, and a liquid binder, which hardens or cures and thereby holds the rubber particles in a solid matrix.
Pre-manufactured products are expensive and difficult to install. Indeed, the installation of pre-manufactured products inevitably results in many seams or joints which can fail in outdoor use. Accordingly, most installations of all-weather surfaces have been of the in situ (formed on site) type. Currently, there are two basic methods of in situ installation, commonly referred to as "dry" and "wet" applied.
The dry method involves spreading dry rubber particulate by hand or by mechanical means over the area to be surfaced. After the rubber is spread, liquid binder (usually an asphalt emulsion or various latex compounds) is sprayed over the particulate at a specified application rate. This process is repeated in succeeding layers of rubber particulate sprayed with binder until the desired surface thickness is achieved.
The wet application process involves mixing rubber particulate with liquid binder in a mixer at specific ratios and batch sizes. The resulting slurry is spread onto the area to be surfaced by hand or mechanical means. This application is usually done in multiple layers when using latex binder and in one mechanically paved layer when using urethane binders.
The wet and dry methods of application have the disadvantage of being labor intensive and time consuming. In addition, the dry application method has the further disadvantage of being too dependent on the experience of the applicator. In particular, improper application renders surfaces installed by this method prone to inconsistent results which are manifested in weak or easily abraded areas of the surface, whereas experienced applicators are better able to insure complete and total encapsulation of the rubber particulate and thus avoid the above problems.
In view of the added difficulties associated with the dry application method, various attempts have been made to devise continuous wet application methods rather than batch.
One such method involves the mixing of urethane binders with rubber granules (usually at a ratio, by weight, of 60% binder, 40% rubber), pumping the mixture through a hose and spraying it through an orifice onto the substrate. However, this type of application, which is known in the art as a structural spray method, is limited to a particle size of approximately 2 mm, and requires a high ratio of binder. Attempts have been made to use this method with latex binders, however there is a tendency for the rubber to separate from the liquid and clog the hose. Moreover, even with latex binders the particle size is limited to a maximum of 2 mm. With rubber particle sizes larger than 2 mm, the velocity of the rubber exiting the tip of the spray nozzle was such that the rubber "bounced" when impacting the substrate, thereby separating the rubber from the liquid binder. Hence, this method is inappropriate for surfaces with greater than 2 mm in depth because of the man-hours required for application of thicker surfaces. In addition, the rubber and binder are mixed in a hopper, and unless conveyed to the site of application promptly, may set prematurely either in the hopper, the hose, or the spray nozzle.